So, I hope you can now see that circumstances can change the situation where use of violence, which would not have been right, now becomes a moral thing to do. This is not based upon your trying to justify your actions, but upon the actions of the person who chose to initiate force against you. Once he does that your response is not an attack, although it may include the use of force. He initiated the force; you responded. He attacked, you reacted. The given circumstances dictate whether the violence which ensues is an "attack" or not. Force? Yes. Violence? Yes. Attack? No. Because YOU did not "start it". That is the key.